1. Field of the Invention
This invention relates to the accurate (with respect to gas mass) high rate filling of pressurized vessels, particularly hybrid/pressurized air bag inflators, regardless of the initial temperature or volume of the pressure vessel being filled.
2. The Related Art
Present-day automotive vehicles incorporate one or more inflatable air bags for the protection of occupants in the event of a crash. The air bags are mounted in a folded compact condition in cooperative relation with a gas inflator. Upon sensing an impending vehicle crash, the inflator produces inflation gas which rapidly inflates and deploys the air bag.
Many types of inflators have been disclosed in the art for use in inflating air bags in such vehicular crash protection or safety restraint systems. One involves the utilization of a quantity of stored compressed inflation gas which is selectively released to inflate the air bag. Another derives a gas source from a combustible gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the air bag. In a third type, the air bag inflating gas results from a combination of stored compressed gas and gas generating material. The last mentioned type is commonly referred to as an augmented gas or hybrid/pressurized inflator.
The pressurized supply of gas is a very important part of a hybrid safety restraint system. The pressurized vessel typically is pressurized with an inert gas such as argon, or a mixture of argon and another inert gas, to approximately 3000 psi at room temperature. In general, the invention is applicable to compressed gases. The phrase compressed gases is understood to encompass inert, flammable and non-flammable gases, either existing alone or in certain proportions. This limit is illustrative only and is not intended in any manner to place restrictions on the scope of the claimed invention.
In the high rate filling of pressurized vessels, a procession of vessels having a variable temperature and variable volume are moved along a production line to a gas filling station. The gas filling station is required to fill each vessel with exactly the same mass of gas and to seal it in a very short cycle time. The measurement of pressure inside the vessel during the filling time to determine if the vessel is filled to the proper mass of gas is not accurate since variations in vessel temperature and volume yield different pressures at the proper mass fill point. The heating effects of high rate filling also change the gas temperature. This makes pressure measurements unreliable in establishing accurate vessel mass fill. Weighing each vessel during the fill process is also not acceptable due to interface loads of the fill machine during the high rate fill process which taint weight measurements during the fill.
There is a need and a demand for countering and correcting these problems that are encountered in the high rate filling of pressure vessels, particularly hybrid/pressurized air bag inflators, with a consistent fill mass.